In a double twister, the function of imparting a tension to yarn is one important function having an influence on formation of balloons and occurrence of yarn breakage and fluffs. The quantity of tension to be applied should be appropriately set according to the yarn speed, spindle rotation number and the properties and fineness of yarn. Moreover, strictly speaking, a delicate attention should be paid so that the quantity of tension to be applied is adjusted according to the quantity of yarn unwound from the cop.
As the tenser, there have ordinarily been used a ball tenser comprising a ball and a ball seat, a washer tenser comprising a washer and a washer receiver, and a tension device constructed by combining both these tensers. However, these conventional tensers are defective and insufficient in various points. For example, delicate adjustment is impossible, or if possible, the cop should be taken out every time adjustment is made. Moreover, the mechanism of prior tensers is complicated and troubles and disorders are readily caused. Furthermore, the life of the tensioning mechanism is much limited.